Aqueous coating composition

ABSTRACT

An aqueous coating composition and a method of coating a metal substrate are provided. The composition and method are particularly suitable for use in coating can bodies and can ends or for-can side seam coatings. The coating composition includes a solvent component and a film forming component. The solvent component includes water and an organic solvent. The film forming component includes a curing agent and the product of the reaction of a carboxy addition polymer and an epoxy resin in the presence of a tertiary amine catalyst.

"This is a Continuation of application Ser. No. 08/618,542, filed Mar.4, 1996 now abandoned, which is a Divisional of application Ser. No.08/317,384, filed Oct. 4, 1994, U.S. Pat. No. 5,527,840 whichapplication(s) are incorporated herein by reference."

BACKGROUND OF THE INVENTION

Coatings are applied to the interior of metal food and beverage cans toprevent the contents from coming into contact with the metal surfaces ofthe containers. Contact of the can contents with the metal surface,especially where acidic products such as soft drinks, tomato juice orbeer are involved, can lead to corrosion of the metal container andresulting contamination and deterioration of the contents. Can interiorsare typically coated with a thin thermoset film to protect the interiormetal surface from its contents. Synthetic resin compositions whichinclude vinyls, polybutadiene, epoxy resins, alkyd/aminoplast andoleoresinous materials have typically been utilized as interior cancoatings. These heat-curable resin compositions are usually applied assolutions or dispersions in volatile organic solvents.

The ideal coating should have low extractables to avoid contamination ofthe contents and should cure rapidly to facilitate can manufacture. Thecured coating should be highly resistant to a wide variety of foodproducts, both under storage and processing conditions. The interiorcoating should be substantially free of blisters and should have goodadhesion to the metal surface, both on application and after processing.

Relatively thick films are required to ensure complete coverage of themetal and to protect the metal during drawing and forming operations.This is especially true of coatings applied to metal substrates used toproduce the end of a can, where film weights of about 5 to about 9mg/in² are typically required. Side seam coatings, which are alsoapplied as thick films and require blister resistant coatings, havesimilar performance characteristics. The coatings used for food cans andcan ends are generally applied and cured into films on high speedcoating lines (e.g., coil coating lines). Modern high speed coatinglines require a coating material that will dry and cure without defectswithin a few seconds as it is heated very rapidly to peak metaltemperatures of about 450° F. to about 550° F. (about 230° C. to about300° C.).

Due to the rapid curing speeds involved, attempts to utilize aqueouscoatings on modern coil coating lines have encountered particularlydifficult problems in avoiding blistering. Blistering typically occursas cure temperature passes through the boiling point of water.Blistering becomes more acute as the thickness of the uncured coatinglayer increases and at higher heating rates and higher peak metaltemperatures. All of these factors may be present during application ofa coating to can ends on a high speed coating line.

Compositions in which the film producing material is dispersed ordissolved in organic solvents are generally used in coating applicationswhere a relatively thick coating is required. Due to environmental andeconomic drawbacks associated with the use of organic solvents, however,there is an increasing demand for aqueous-based coatings. In addition tobeing less expensive than organic solvent-based coatings, aqueous-basedcoatings minimize the environmental impact of organic solvent releaseand diminish the need to incinerate curing oven effluents.Unfortunately, under rapid, high temperature curing conditions,currently available aqueous-based coatings do not provide satisfactoryperformance. There is, accordingly, a continuing need for aqueous-basedcoatings, which will permit the formation under rapid, high temperaturecuring conditions of protective films which are substantially free ofblisters.

SUMMARY OF THE INVENTION

The present invention provides an aqueous coating composition capable offorming a tough coating, resistant to hydrolysis and other forms ofchemical attack, while minimizing environmental problems associated withthe use of organic solvents. The coating composition can be applied andcured without blistering at high coating weights and high line speeds toprovide a resilient, corrosion resistant, cured film. In addition to thechoice of specific components, achievement of these properties isdependent on a proper balance of the solids content, viscosity and watercontent of the coating composition.

The coating composition includes a solvent component and a film formingcomponent. The solvent component includes water and an organic solvent.The film forming component includes a curing agent and the product ofthe reaction of a carboxy addition polymer and an epoxy resin in thepresence of a tertiary amine catalyst.

The present invention also provides a method of coating a metalsubstrate to provide a cured film on at least one surface of thesubstrate. The method includes applying the aqueous coating compositiononto the surface of the metal substrate to form a coating layer. Thecoated metal substrate is then heated so that the coating layer cures toform a cured film adhered to the substrate surface. The coated metalsubstrate is typically cured by heating for about 2 to about 20 secondsin an oven at a temperature of about 230 to about 300° C. The cured filmis substantially free of blisters and typically has a film weight of atleast about 5 mg/in² and, preferably, about 7 mg/in² to about 9 mg/in².

The present invention also provides a composite material which includesa metal substrate having at least one surface covered with a cured film,which is the result of coating the substrate surface with theabove-described coating composition and heating the coated metalsubstrate for 2 to 20 seconds at a temperature of 230 to 300° C. Thecured film preferably has a film weight of at least about 5 mg/in².

DETAILED DESCRIPTION OF THE INVENTION

Coating compositions of this invention are useful for protecting theinterior of food and beverage cans. The cans are typically formed frommetals such as aluminum, tin, steel or tin-plated steel. The coatingsare generally applied to metal sheets by one of two processes, each ofwhich involves different coating and curing conditions. The coated metalsheets may be fabricated into can bodies or ends in a later stage of themanufacturing operation. One process, called the sheet bake process,involves roll coating large metal sheets. These sheets are then placedup-right in racks and the racks are typically placed in ovens for about10 minutes to achieve peak metal temperatures of about 180° C. to about205° C. In a coil coating process, the second type of process, largerolls of thin gage metal (e.g., steel or aluminum) are unwound, rollcoated, heat cured and rewound. During the coil coating process, thetotal residence time in the curing ovens will vary from about 2 secondsto about 20 seconds with peak metal temperatures typically reachingabout 230° C. to about 300° C.

The aqueous coating composition of the present invention is particularlysuitable for use in coating the ends or closures of food and beveragecans or for can side seam coatings. Can ends are typically roll coatedon coil coating lines to a dry film weight (after curing) of at leastabout 5 mg/in², preferably about 7 to about 9 mg/in², and mostpreferably about 7.5 to about 8.5 mg/in². The present coatingcomposition may also be used to coat the interior of the can body, whereit typically is applied via a sheet bake process.

The present aqueous coating composition can be coated onto a metalsubstrate at a relatively high film weight (e.g., 5 to 9 mg/in²). Theintegrity and thickness of the uncured film can be sustained despite theexposure of the coated substrate to translational forces (e.g., thetranslational forces generated during the coating of large rolls of thingage metal on high speed coil coating lines). The coated substrate canthen be cured at high coating weights and high line speeds withoutforming blisters. Use of the present coating composition permitsformation of a tough, resilient cured film which is substantially freeof defects. Another advantage of the present aqueous coating compositionis that, despite differences in performance requirements between the twoprocesses, the same composition used to form a relatively thick coatingvia a coil coating process may also be employed to form thinner coatings(e.g., a film weight of 3-4 mg/in²) through a sheet bake process. Thisavoids the need to develop separate formulations to address thediffering requirements of the two application methods.

The aqueous coating composition includes at least about 50 wt. % and,preferably, at least about 55 wt. % of a solvent component and at leastabout 30 wt. % of a film forming component (based on total weight of thecoating composition). The aqueous coating composition must havesufficient viscosity and solids content to permit application at arelatively high film weight (e.g., 5 to 9 mg/in²) on a metal substratesubjected to translational forces, such as the forces generated during acoil coating process. Viscosity of the coating composition must also below enough to avoid blistering during cure of the coated substrate.Preferably, viscosity of the coating composition is about 13 to about100 seconds, more preferably about 20 to about 80 seconds and mostpreferably about 30 to about 60 seconds (#4 Ford cup at 80° F. (27°C.)). Where the coating composition is to be applied through a coilcoating process, the composition preferably includes at least about 30wt. % and, more preferably, about 35 to about 45 wt. % of film formingcomponent and typically has a viscosity of about 30 to about 60 seconds(#4 Ford cup at 80° F). For those applications where a sheet bakeprocess is to be utilized and relatively low coating weight (e.g., 3-4mg/in²) are desired, the composition preferably includes about 35 toabout 45 wt. % of film forming component and typically has a viscosityof about 50 to about 80 seconds (#4 Ford cup at 80° F).

The coating composition is in the form of an aqueous dispersion with thefilm forming component substantially present in the form of particles.If particle size is too large, stability problems may be experiencedwith the dispersion. Typical particle size is about 0.1 to about 0.6micron, preferably about 0.2 to about 0.4 micron and, most preferably,no more than 0.35 micron. The pH of the coating composition ispreferably within the range of about 6.0 to about 8.0 and morepreferably is about 6.5 to about 7.5.

The solvent component includes water and an organic solvent. Preferably,the solvent component includes about 70 to about 97 wt. % , morepreferably about 75 to about 95 wt. % water and most preferably about 79to about 91 wt. % water (based on the total weight of the solventcomponent). In order to minimize cost and environmental problems, it isdesirable to include as high a percentage of water as possible. Someorganic solvent is necessary, however, to prevent formation of blistersduring curing, particularly where the coating is applied on a high speedcoil coating line. The solvent component typically includes at leastabout 3 wt. %, preferably at least about 5 wt. % and more preferably atleast about 8 wt. % organic solvent (based on total weight of thesolvent component).

Preferably the organic solvent is substantially miscible with water andis either in the form of a singular polar compound or as a mixture ofcompounds which may include non-polar components. The solvent typicallyis capable of dissolving the resins in the film-forming component,thereby facilitating their dispersion in an aqueous solution. Suitablesolvents, to be used either alone or as part of a mixture, includeglycol ethers and alcohols such as alkanols, monoalkyl glycols, andalkyl carbitols (diethylene glycol monoalkyl ethers). Among the mostcommonly used solvents are alcohols such as butyl alcohols (e.g.,n-butanol), 2-butoxyethanol, Butyl Carbitol (diethylene glycol monobutylether). Non-polar solvents may also be included as minor constituents ofthe organic solvent. Suitable non-polar solvents which may be usedinclude: aliphatic and aromatic hydrocarbons, such as naphtha, heptane,mineral spirits, toluene and the like.

The film forming component includes a carboxy addition polymer and anepoxy resin, which have been reacted together in the presence of atertiary amine catalyst. A curing agent is then blended with theresulting reaction product. The amounts (wt. %) specified for thecarboxy addition polymer, the epoxy resin and the curing agent isexpressed as a wt. % based on the total weight of the carboxy additionpolymer (CAP) plus the epoxy resin (ER) plus the curing agent (CA).

The resin mixture includes at least about 10 wt. %, preferably about 15to about 40 wt. % of the carboxy addition polymer (based on the totalweight of CAP+ER+CA). Most preferably, the resin mixture includes atleast about 15 to about 25 wt. % of the carboxy addition polymer.

The carboxy addition polymer may be prepared by conventionalpolymerization processes and is preferably a copolymer of at least onepolymerizable, ethylenically unsaturated carboxylic acid monomer and atleast one copolymerizable nonionic monomer. Suitable ethylenicallyunsaturated carboxylic acid monomers include acrylic, methacrylic,maleic, fumaric and itaconic acids. The ethylenically unsaturatedcarboxylic acid monomer is preferably an α,β-unsaturated carboxylic acidhaving from 3 to 10 and, more preferably, from 3 to 5 carbon atoms.Acrylic acid and methacrylic acid are particularly preferred. Suitablecopolymerizable nonionic monomers include nonionic ethylenicallyunsaturated monomers, such as vinyl aromatic compounds and alkyl estersof ethylenically unsaturated carboxylic acids. Included among the mostcommonly used copolymerizable nonionic monomers are lower alkylacrylates (e.g., ethyl acrylate), lower alkyl methacrylates, styrene,alkyl-substituted styrenes, vinyl acetate and acrylonitrile. Preferably,the copolymerizable nonionic monomer is selected from the groupconsisting of styrene and C₁, to C₆ alkyl esters of α,β-unsaturatedcarboxylic acids having 3 to 5 carbon atoms.

The weight average molecular weight of the carboxy addition polymer isgenerally at least about 5,000 and should not exceed about 60,000. Morepreferably, weight average molecular weight of the addition polymer isabout 5,000 to about 25,000 and most preferably, about 7,000 to about15,000. The carboxy addition polymer has an acid number of at leastabout 165, typically about 200 to about 350, and preferably about 225 toabout 325. The acid number is defined as the amount of potassiumhydroxide (in mg) required to neutralize one gram of polymer (on asolids basis). Typically, the carboxy addition polymer has a glasstransition temperature (T_(g)) of no more than about 110° C. and,preferably, the glass transition temperature of the carboxy additionpolymer is about 50 to about 100° C. If the coating composition includesa relatively large amount of epoxy resin (e.g., at least about 60 wt. %based on the total weight of CAP+ER+CA), a carboxy addition polymerhaving a relatively low T_(g), i.e., about 50 to about 100° C., istypically employed.

The resin mixture also includes at least about 40 wt. %, preferablyabout 50 to about 85 wt. % of the epoxy resin (based on the total weightof CAP+ER+CA). Most preferably, the resin mixture includes about 60 toabout 80 wt. % of the epoxy resin. The epoxy resin may be any organicsolvent-soluble resin containing epoxy groups. Preferably, the epoxyresin includes glycidyl polyethers having more than one epoxide groupper molecule (i.e., glycidyl polyethers containing an average of greaterthan 1.0 epoxy groups per molecule). Typically, the glycidyl polyethershave an average of about 2.0 to about 2.5 epoxide groups per molecule.Diglycidyl ethers of dihydric phenols are particularly suitable for usein the present coating composition. Exemplary dihydric phenols includeresorcinol, 1,5-dihydroxy naphthalene and bisphenols, such as BisphenolA (p,p'-dihydroxy-2,2-diphenyl propane). Bisphenol A is the preferreddihydric phenol. The epoxy resins typically used in the presentinvention may be derived from the reaction of the dihydric phenol, andan epihalohydrin, such as epichlorohydrin. Molecular-weight of theinitial reaction product may be increased by reaction with additionaldihydric phenol. Epoxy resins suitable for use in the present inventiontypically have epoxide equivalent weights of at least about 1,000 and nomore than about 5,000. Preferably, the epoxide equivalent weight isabout 1,500 to about 4,000. Diglycidyl ethers of Bisphenol A arecommonly available in commerce and commercial materials such as Epon1009F and Epon 1007F (both available from Shell Chemical Company,Houston, Tex.) are suitable for use in the present invention. Mostpreferably, the epoxy resin includes a diglycidyl ether of Bisphenol Ahaving an epoxide equivalent weight of about 1,500 to about 3,500. Ifthe coating composition contains a relatively small amount of curingagent (e.g., no more than about 10 wt. % based on the total weight ofCAP+ER+CA), the epoxy resin preferably includes a diglycidyl ether ofBisphenol A having a relatively high epoxide equivalent weight, e.g.,about 2,500 to about 3,500. Coating compositions which contain arelatively large amount of epoxy resin (e.g., at least about 60 wt. %based on the total weight of CAP+ER+CA), also preferably include arelatively high epoxide equivalent weight (e.g., about 2,500 to about3,500) diglycidyl ether of Bisphenol A.

The epoxy resin may also be partially defunctionalized by reaction witha phosphorus-containing acid or with an organic monoacid. Thephosphorus-containing acid is an acid having a P-OH functionality or anacid that is capable of generating such a functionality upon reactionwith water (e.g., a compound having a P-O-P functionality). Examples ofsuitable phosphorus-containing acids include polyphosphoric acid,superphosphoric acid, aqueous phosphoric acid, aqueous phosphorous acidand partial alkyl esters thereof. The organic monoacid is preferably anaromatic carboxylic acid having up to ten carbon atoms or a C₁ to C₂₀alkanoic acid. Examples of suitable organic moncacids include acetic,benzoic, stearic, palmitic and octanoic acids. The epoxy resin istypically defunctionalized by reacting from up to about 50% of the epoxygroups present with the organic monoacid. Where the epoxy resin isdefunctionalized by reaction with the phosphorus-containing acid, up toabout 50% of the epoxy groups are typically reacted with the acid.

The reaction between the carboxy addition polymer and the epoxy resin iscarried out in the presence of about 0.35 to about 1.0 equivalents and,more preferably, about 0.5 to about 0.8 equivalents, of a tertiary aminecatalyst per equivalent of carboxy groups present in the carboxyaddition polymer. Examples of suitable tertiary amines include trialkylamines (e.g., diethylbutyl amine), dialkyl benzyl amines, and cyclicamines such as N-alkyl pyrrolidine, N-alkyl morpholine and N,N'-dialkylpiperidine. Tertiary amines containing at least two methyl groups, suchas dimethyl ethanolamine, trimethylamine and dimethylbenzyl amine, arepreferred.

The film forming component includes at least about 2 wt. % the curingagent (based on the total weight of CAP+ER+CA). More preferably, thefilm forming component includes about 3 to about 45 wt. %, and mostpreferably, about 5 to about 25 wt. % of the curing agent. The curingagent includes at least one resin selected from the group consisting ofaminoplast resins and phenoplast resins. The curing agent preferablyincludes a phenoplast resin. Phenoplast resins are condensation productsof an aldehyde, such as formaldehyde or acetaldehyde, and a phenol.Suitable phenoplast resins may be derived from an unsubstituted phenol,cresol or other alkyl phenols as well as from dihydric phenols such asBisphenol A. Mixtures of phenols may be used to vary and controlproperties of the phenoplast resin. The phenoplast resin preferablyincludes at least one of an alkylated phenol-formaldehyde resin and abisphenol A-formaldehyde resin. The melting point of the phenoplastresin is preferably no more than about 100° C. Alkylatedphenol-formaldehyde resins which are suitable for use in the presentcoating compositions include polymeric, solid resins having low colorand a molecular weight of at least 1000. Such alkylatedphenol-formaldehyde resins are typically based on one or more longerchain alkylated phenols, e.g., phenols substituted with an alkyl grouphaving from 4 to 10 carbon atoms. Representative longer chain alkylatedphenols include t-butylphenol, hexylphenol, octylphenol, t-octylphenol,nonylphenol, decylphenol and dodecylphenol.

Depending upon the desired application, the coating composition mayinclude other additives such as lubricants, coalescing solvents,leveling agents, wetting agents, thickening agents, suspending agents,surfactants, defoamers, adhesion promoters, corrosion inhibitors,pigments and the like. Coating compositions, which are to be used as acan coating, typically include a lubricant such as a hard, brittlesynthetic long-chain aliphatic wax, a carnuba wax emulsion, or apolyethylene/Teflon™ blend.

The coating composition of the present invention may be prepared byconventional methods. For example, the coating composition may beprepared by adding the epoxy resin to a solution of the carboxy additionpolymer in a solvent mixture which includes an alcohol and a smallamount of water. During the addition, an inert gas blanket is maintainedin the reactor and the solution of the carboxy addition polymer iswarmed, typically to about 100° C. The mixture is maintained at thattemperature and stirred until the epoxy resin is dissolved. The tertiaryamine (e.g., dimethylethanol amine) is then added and the resultingmixture stirred for a period of time at elevated temperature. The curingagent, which typically includes a phenoplast resin, is then added andthe batch is held for roughly 30 minutes at a temperature of about 90 to100° C. Deionized water is added under maximum agitation to emulsify theresin and the temperature is allowed to drop. Additional deionized wateris typically added at a uniform rate over a period of about one hourwhile the batch is cooling. The final viscosity is adjusted to thedesired value (typically 30-60 seconds (#4 Ford cup at 80° F.) byfurther addition of deionized water. The coating composition that isproduced may be used as is or other additives (e.g., a lubricant) may beblended in to form the final coating composition.

The present invention also provides a method of coating a metalsubstrate to provide a substantially continuous film on at least onesurface of the substrate. The method includes applying the abovedescribed aqueous coating composition onto the metal surface to form acoating layer and heating the coated substrate so that the coating layercures to form a cured film which adheres to the substrate surface. Thecured film has a film weight of at least about 3 mg/in², preferably atleast about 5 mg/in², and is substantially free of blisters. The presentcoating compositions are typically used to produce blister free curedfilms having films weights of about 7 mg/in² to about 9 mg/in². Thecoating composition may be applied to the substrate surface using avariety of well-known techniques. For example, the composition may beroll coated, bar coated or sprayed onto the surface. Where large rollsof thin gauge metal are to be coated, it is advantageous to apply thecoating composition via reverse roll coating. Where large metal sheetsare to be coated, the coating composition is typically direct rollcoated onto the sheets as part of a sheet-bake process. The sheet-bakeprocess is typically used to form a coated metal substrate where arelatively low (e.g., about 3-4 mg/in²), cured film weight is desired.If the coating is applied using a sheet-bake process, the coated metalsubstrate is typically cured at a temperature of about 180° C. to about205° C. for about 8 to about 10 minutes. In contrast, when the coatingis carried out using a coil-coating process, the coated metal substrateis typically cured by heating for about 2 to about 20 seconds at atemperature of about 230° C. to about 300° C. If the coil-coatingprocess is used to produce material to be fabricated into can ends, thecured film on the coated metal substrate typically has a film weight ofat least about 5 mg/in² and preferably, about 7 to about 9 mg/in².

The present invention may be further described by reference to thefollowing examples. Parts and percentages, unless otherwise designated,are parts and percentages by weight.

EXAMPLES Example 1

Carboxy Addition Polymer A

A five liter reactor was fitted with stirrer, condenser, heater, andthermometer with inert gas inlet. An inert gas blanket was introduced tothe reactor. n-Butanol (3636 parts) and 403 parts deionized water werecharged to the reactor and the solvent mixture was heated underagitation to reflux (95-97° C.). In a separate vessel, a monomer premixwas prepared from 1160 parts ethyl acrylate, 1864 parts acrylic acid,2480 parts styrene and 432 parts 70% benzoyl peroxide. The monomerpremix was added to the reactor over four hours while maintaining thetemperature at 95-97° C. After the addition was complete, the batch wascooled to 93° C. and held at that temperature for one hour. After theone hour hold period, 31 parts 70% benzoyl peroxide were added and thebatch was held for another two hours at 93° C. to ensure completereaction. The final product had an acid number of 248 and contained 57.9wt. % nonvolatile components.

Examples 2-7

Carboxy Addition Polymers B-G

Using a similar procedure to that described in Example 1, a solution ofa carboxy addition polymer (CAP) in 3636 parts n-butanol and 403 partsdeionized water was prepared from ethyl acrylate, styrene and eitheracrylic acid or methacrylic acid (the parts by weight of the monomersused to prepare each specific CAP are shown in Table 1) with 463 parts70% benzoyl peroxide. The final products were characterized as shown inTable 1.

Example 8

Coating Composition 1

A reaction flask was prepared with a stirrer, condenser, heater andthermometer with an inert gas inlet. An inert gas blanket was introducedand 112.6 parts Epon 828 (Shell Chemical; Houston, Tex.), 59.4 partsBisphenol A, 9.1 parts diethylene glycol monobutyl ether (ButylCarbitol) and 0.15 parts ethyltriphenylphosphonium iodide were chargedto the reactor. The mixture was heated with agitation to 121° C. andallowed to exotherm to 170-180° C. Following the exotherm, the batch washeld at 155-160° C. until an epoxy value of 0.050 was attained. Then16.0 parts diethylene glycol monobutyl ether was added. Then 155.0 partsof the solution of the carboxy addition polymer from Example E was addedand the temperature was allowed to drop to 96° C. The batch was stirredto achieve uniformity. After the batch was uniform, dimethylethanolamine (22.0 parts) was added at a uniform rate and the batch was heldfor thirty minutes at 90-98° C. An exotherm was seen immediatelyfollowing the amine addition. After the thirty minute hold, 86.0 partst-butylphenol-formaldehyde resin (average degree of polymerization of 6)was added and the batch was stirred for thirty minutes at 90-98° C. Theheat was then turned off and 103 parts deionized water were added at auniform rate to emulsify the resin. The batch was held for one hour,then 240 parts deionized water were added over one hour at a uniformrate. The resulting epoxy/acrylate/phenolic composition contained 4.19wt. % nonvolatile components.

The epoxy/acrylate/phenolic composition (100 parts) from above wascharged to a mixing vessel equipped with an agitator. Deionized water,7.44 parts, was added under agitation and mixed until uniform. Theresulting coating composition had a theoretical nonvolatile component of39.0 wt. %.

Example 9

Coating Composition 2

A 1 liter reaction flask was fitted as described in Example 8 and 247parts of the carboxy addition polymer prepared in Example E was charged.The resulting mixture was heated with agitation to approximately 100° C.under an inert gas blanket. Epon 1009F epoxy resin (Shell Chemical;Houston, Tex.; 138 parts) was added to the reaction flask and themixture was stirred at 100° C. until the epoxy resin dissolved. Afterthe batch was uniform, stirring was continued until the batch was 96° C.Dimethylethanol amine (32.0 parts) was then added at a uniform rate andthe resulting mixture was stirred for thirty minutes at a temperature of90-98° C. t-butylphenol-formaldehyde resin (average degree ofpolymerization of 6; 68.8 parts) was then added. The batch was heldthirty minutes at 90-98 °C. and 94 parts deionized water was added undermaximum agitation to emulsify the resin. The temperature was allowed todrop to 80-82° C. while the batch was held for sixty minutes. The heatwas turned off and deionized water (220 parts) was added at a uniformrate over one hour and the batch was allowed to cool. The resultingepoxy/acrylate/phenolic composition had a nonvolatile content of 43.1wt. %.

The epoxy/acrylate/phenolic composition (100 parts) was charged to amixing vessel equipped with an agitator. Deionized water (13.4 parts)was added under agitation and mixed until uniform to produce a coatingcomposition with a theoretical nonvolatile component of 38.0 wt. %.

Examples 10-31

Coating Compositions 3-20

Using a procedure similar to that described in either Examples 8 and 9,coating composition 3-20 were prepared from a t-butylphenol-formaldehyderesin (average degree of polymerization of 6) and the carboxy additionpolymers and epoxy resins indicated in Table II.

Two of the epoxy resins used, Epon 1009F and Epon 1007F, were obtainedfrom a commercial source. Epon 1009F (Shell Chemical Company, Houston,Tex.) is an epoxy resin derived from Bisphenol A and epichlorohydrinhaving an epoxide equivalent weight of about 3000 and an epoxy value of0.026-0.043. Epon 1007F (Shell Chemical Company, Houston, Tex.) is anepoxy resin derived from Bisphenol A and epichlorohydrin having anepoxide equivalent weight of 1700-2300 and an epoxy value of0.043-0.059.

The other epoxy resins were obtained by reacting a commercial epoxyresin (Epon 828) with Bis-phenol A. Epon 828 (Shell Chemical Company,Houston, Tex.) is an epoxy resin derived from Bisphenol A andepichlorohydrin having an epoxide equivalent weight of 185-192 and anepoxy value of 0.52-0.54. Epoxy resin H is an epoxy resin having anepoxy value of 0.038 and was obtained by reacting Epon 828 and BisphenolA (in a weight ration of 64.80/35.20) using the procedure described inExample 8. Epoxy resin M is an epoxy resin having an epoxy value of0.050 and was obtained by reacting Epon 828 and Bisphenol A (in a weightration of 65.65/34.35) as described in Example 8. Epoxy resin L is anepoxy resin having an epoxy value of 0.115 and was obtained by reactingEpon 828 and Bisphenol A (in a weight ration of 70.25/29.75) using theprocedure described in Example 8.

In each instance, the carboxy addition polymer and epoxy resin werereacted by heating after the addition of dimethylethanol amine catalyst(0.65 equivalent per equivalent of carboxy groups present in the carboxyaddition polymer). The t-butylphenol-formaldehyde resin was then addedfollowed by dilution with water as described in Examples 8 and 9 to forman intermediate coating composition. The coating compositions based oneither Epon 1009F or Epon 1007F were prepared in a n-butanol/watersolvent system according to the procedure described in Example 9. Thecoating compositions based on either Epoxy Resin H, Epoxy Resin M, orEpoxy Resin L were prepared in a Butyl Carbitol/n-butanol/water solventsystem according to the procedure described in Example 8. The wt. %nonvolatile components (solids), viscosity, pH and particle size foreach of the intermediate coating compositions are shown in Table III.

The intermediate coating compositions described above were diluted withwater (where necessary) to obtain a final coating composition having aviscosity and wt. % solids within the desired ranges (viscosity--about30 to about 60 seconds (#4 Ford cup at 80° F.); about 30 to about 45 wt.% solids). Using an appropriately sized barcoater, each of coatingcompositions 1-20 were applied to aluminum metal panels to form a"blister panel." The blister panels were cured by baking for 10 secondsin a 450° F. oven (peak metal temperature of 450° F.) to produce curedcoated metal panels having a cured film weight of 7.5 to 8.0 mg/in². Thecured coated metal panels were evaluated for the formation of blisters.The results of these evaluations are summarized in Table II. The resultsshown in Table II demonstrate that the aqueous coating compositions ofthe present invention are capable of being applied at high coatingweights and cured at high line speeds without blistering to provide aresilient, cured film.

Particle Size Determinations

The measurement of the average particle size of the polymericdispersions reported in Table III were carried out using a Spectronic 20Bausch & Lomb 33-39-61-62 spectrophotometer. About one-half to one dropof the coating composition under evaluation was added to 50 ml distilledwater. The sample cell of the spectrophotometer was filled from 1/4 to1/2 full with the resulting solution. The solution was then furtherdiluted by adding distilled water to fill approximately 3/4 of the cell.After shaking the cell to produce a homogeneous solution, the percenttransmittance of the diluted solution was measured at a wavelength of375 millimicrons. The concentration of dispersed polymer in the solutionwas then adjusted so that the solution had an optical density between0.50 and 0.54 at 375 millimicrons. The optical density of the solutionwas then measured at 375, 450, 500 and 550 millimicrons. For eachsolution, log(optical density) was plotted versus log(wavelength) andthe average particle size was determined from the slope of the plot,where ##EQU1## and

    Average Particle Size=Antilog[0.055-0.2615(Slope)].

Viscosity Measurements

For the purposes of this application, #4 Ford cup viscosity wasdetermined using a slightly modified version of ASTM D-1200-54, which isa procedure used for determining the viscosity of paints, varnishes andrelated liquid materials. The procedure is carried out with a #4Ford-type efflux viscosity cup (available from Scientific InstrumentCo., Detroit, Mich.). The liquid material (as a solution or dispersion)and the #4 Ford cup are brought to a constant temperature of 80° F. Theorifice at the bottom of the viscosity cup is closed and the liquidmaterial to be tested is then poured into the viscosity cup to a slightoverflowing of the inner cup. After any excess material is allowed toflow into the outer cup, the orifice at the bottom of the cup is opened.The time interval required for the appearance of the first break in thestream of material flowing from the orifice is measured using astopwatch. The viscosity is reported as the elapsed time to theappearance of the first break in the stream.

In some instances, viscosity was determined using a Brookfield Model LVFviscometer (Brookfield Engineering Laboratories, Inc.). The Brookfieldviscometer measures the torque required to rotate a spindle headimmersed in the coating composition at a given angular velocity. Theviscosity is reported in units of centipoises.

RESISTANCE TO BLISTERING

The coating composition to be evaluated (100-150 g.) was placed in a 9oz. jar and agitated for 20 seconds with a plastic prop attached to ahigh speed motor. The coating composition was then bar coated onto analuminum panel to form a "blister panel" having a 7.5-8.0 mg/in² thickcoating. A "blister panel" is only coated in the middle of the panel.This enables more heat to be applied to the coating and increases theseverity of the blister test.

The coated blister panel is air dried for 5 seconds and then immediatelyplaced in a coil coating oven with a peak metal temperature of 10seconds at 450° F. After removal from the oven, the cured coated panelin water quenched and visually inspected for blisters. The resistance ofthe coating to blistering is rated on a pass/fail scale.

The invention has been described with reference to various specific andpreferred embodiments and techniques. It should be understood, however,that many variations and modifications may be made while remainingwithin the spirit and scope of the invention.

                                      TABLE I                                     __________________________________________________________________________    CARBOXY ADDITION POLYMERS                                                     CARBOXY ADDITION                                                              POLYMER    A    B    C    D    E    F   G                                     __________________________________________________________________________    CONSTITUENTS:                                                                 Acrylic Acid                                                                             1864 --   2189 1412 --   2401                                                                              --                                    Methacrylic Acid                                                                         --   2109 --   --   1814 --  2531                                  Styrene    2480 1130 1654 3064 1429 2323                                                                              2225                                  Ethyl Acrylate                                                                           1160 2259 1654 1022 2254  774                                                                               742                                  PROPERTIES:                                                                   T.sub.g *  67.0 57.5 54.2 70.4 54.8 78.4                                                                              107.6                                 Solids (wt. %)                                                                           57.9 55.4 57.4 57.3 55.6 57.9                                                                              55.4                                  Acid Number                                                                               248  255  294  195  225  326                                                                               305                                  M.sub.W    11,680                                                                             12,660                                                                             10,670                                                                             13,840                                                                             13,360                                                                             9,960                                                                             13,080                                N.sub.N    3,380                                                                              3,570                                                                              2,940                                                                              4,220                                                                              3,860                                                                              2,860                                                                             3,930                                 M.sub.W /M.sub.N                                                                         3.46 3.55 3.62 3.28 3.46 3.48                                                                              3.33                                  __________________________________________________________________________     *Theoretical T.sub.g calculated based on the amount of each monomer in th     terpolymer according to the formula:                                          ##STR1##                                                                      where the wt. % of each monomer is based on the total weight of all three     monomers in the terpolymer; the T.sub.g s are expressed in degrees Kelvin     and T.sub.g (homopolymer X) is the T.sub.g of a homopolymer formed from a     given monomer "X".                                                       

                  TABLE II                                                        ______________________________________                                        COATING COMPOSITIONS                                                          COAT-                                                                         ING                                                                           COM-                              PHENO-                                      POSI- EPOXY   EPOXY   CAP   CAP   LIC                                         TION  TYPE    LEVEL   TYPE  LEVEL LEVEL  BLISTERS                             ______________________________________                                        1     M       50      E     25    25     PASS                                 2     1009/F  40      E     40    20     PASS                                 3     1009/F  53      A     30    17     PASS                                 4     1007/F  53      C     30    17     PASS                                 5     1009/F  53      D     30    17     PASS                                 6     H       60      A     20    20     PASS                                 7     H       60      B     20    20     PASS                                 8     H       60      D     20    20     PASS                                 9     M       60      A     20    20     PASS                                 10    M       60      F     20    20     PASS                                 11    H       70      A     20    10     SLIGHT                               12    H       70      D     20    10     SLIGHT                               13    H       75      A     20    5      PASS                                 14    M       75      C     20    5      FAIL                                 15    1009/F  50      D     40    10     PASS                                 16    L       50      F     25    25     PASS                                 17    1007/F  50      B     30    20     PASS                                 18    H       50      E     30    20     PASS                                 19    H       40      F     15    45     PASS                                 20    H       40      G     15    45     PASS                                 21    1009/F  60      D     35    5      SLIGHT                               22    1007/F  60      G     35    5      FAIL                                 23    H       80      C     15    5      PASS                                 24    H       80      G     15    5      FAIL                                 ______________________________________                                    

                  TABLE III                                                       ______________________________________                                        PHYSICAL CONSTANTS OF                                                         INTERMEDIATE COATING COMPOSITIONS                                             Intermediate                                                                  Coating            Viscosity                                                  Composition                                                                              Solids  (cps)      pH   Part Size                                  ______________________________________                                        1          41.9%   18300      7.0  0.23                                       2          43.1%   8500       7.1  0.57                                       3          43.3%   5560       6.8  0.27                                       4          42.9%   58000      6.5  0.34                                       5          43.4%   6510       7.1  0.28                                       6          42.6%   224        7.0  0.27                                       7          43.0%   96000      7.0  0.23                                       8          42.0%   83         7.4  0.26                                       9          43.4%   9180       7.0  0.26                                       10         41.6%   1300000    6.8  0.25                                       11         43.8%   7520       7.0  0.18                                       12         42.3%   126        7.1  0.18                                       13         44.5%   13700      7.0  0.19                                       14         35.5%   10960      6.8  0.16                                       15         42.6%   1840       7.0  0.40                                       16         35.4%   590000     7.0  0.25                                       17         38.6%   22400      7.0  0.28                                       18         41.7%   3600       7.2  0.37                                       19         41.6%   65         6.7  0.52                                       20         41.7%   565        7.4  0.32                                       21         42.9%   1640       7.3  0.22                                       22         30.6%   8800       7.5  0.14                                       23         38.5%   1848       6.8  0.17                                       24         31.7%   2000       7.7  0.15                                       ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                        COATING COMPOSITION SOLVENT COMPONENTS                                        AND FINAL SOLIDS                                                                     Intermediate                                                           Coating                                                                              Coating    Final Coating Composition                                   Composi-                                                                             Composition                                                                              Solids             Organic                                  tion   Water/Organic                                                                            (Theoretical)                                                                           Water/Organic                                                                          Component*                               ______________________________________                                        1      80.55/19.45                                                                              39.6      82.84/17.16                                                                            BuOH/BuC                                 2      77.46/22.54                                                                              38.0      82.01/17.99                                                                            BuOH                                     3      81.73/18.27                                                                              40.6      84.17/15.83                                                                            BuOH/BuC                                 4      82.68/17.32                                                                              36.6      87.27/12.73                                                                            BuOH/BuC                                 5      80.68/19.32                                                                              40.0      83.30/16.70                                                                            BuOH/BuC                                 6      80.13/19.87                                                                              42.6      80.13/19.87                                                                            BuOH/BuC                                 7      80.13/19.79                                                                              38.0      84.05/15.95                                                                            BuOH/BuC                                 8      79.45/20.55                                                                              42.0      79.45/20.55                                                                            BuOH/BuC                                 9      80.13/19.87                                                                              40.0      82.82/17.18                                                                            BUOH/BuC                                 10     81.98/18.02                                                                              32.0      88.30/11.70                                                                            BuOH/BuC                                 11     80.13/19.87                                                                              40.0      83.11/16.89                                                                            BuOH/BuC                                 12     79.45/20.55                                                                              42.3      79.45/20.55                                                                            BuOH/BuC                                 13     80.13/19.87                                                                              40.0      83.59/16.41                                                                            BuOH/BuC                                 14     85.91/14.09                                                                              32.0      88.01/11.99                                                                            BuOH/BuC                                 15     79.17/20.83                                                                              40.0      81.41/18.59                                                                            BuOH                                     16     87.09/12.91                                                                              30.0      90.02/9.98                                                                             BuOH/BuC                                 17     84.75/15.25                                                                              32.0      88.74/11.26                                                                            BuOH/BuC                                 18     81.30/18.70                                                                              38.0      84.10/15.90                                                                            BuOH/BuC                                 19     80.07/19.93                                                                              41.6      80.07/19.93                                                                            BuOH/BuC                                 20     79.86/20.14                                                                              40.0      81.28/18.72                                                                            BuGH/BuC                                 21     81.36/18.64                                                                              40.0      83.56/16.44                                                                            BuOH/BuC                                 22     88.57/11.43                                                                              28.0      89.97/10.03                                                                            BuOH                                     23     82.89/17.11                                                                              36.0      84.68/15.32                                                                            BuOH/BuC                                 24     86.99/13.01                                                                              31.7      86.99/13.01                                                                            BuOH/BuC                                 ______________________________________                                         *BuOH -- nButanol                                                             BuC -- nButyl Carbitol                                                   

what is claimed is:
 1. A method of coating a metal substratecomprising:a) applying an aqueous coating composition onto at least onesurface of the metal substrate to form a coating layer on the surface,wherein the aqueous coating composition comprises at least about 30 wt.% (based on the weight of the coating composition) of a film formingcomponent which includes:A) a product formed by reacting a carboxyaddition polymer and an epoxy resin in the presence of a tertiary amine,wherein the carboxy addition polymer has a theoretical glass transitiontemperature of no more that about 110° C., and an acid number of atleast about 200, and the epoxy resin had an epoxide equivalent wt. of atleast about 1500; and B) a phenoplast resin having a melting point of nomore than about 100° C.; wherein the composition has a viscosity ofabout 30 to about 60 seconds determined by #4 Ford cup at 80° F.; and b)heating the coated metal substrate such that the coating layer forms acured film.
 2. The method of claim 1 wherein the film forming componentincludes:A) a product formed by reacting at least about 10 wt. % of thecarboxy addition polymer and at least about 40 wt. % of the epoxy resin,wherein the epoxy resin has an epoxide equivalent wt. of about 1500 toabout 5000 in the presence of the tertiary amine; and B) at least about2 wt. % of the phenoplast resin; the wt. % of the carboxy additionpolymer, the epoxy resin and the phenoplast resin being based on thetotal weight of the carboxy addition polymer plus the epoxy resin plusthe phenoplast resin; and wherein the carboxy addition polymer and theepoxy resin are reacted in the presence of about 0.35 to about 1.0equivalents of the tertiary amine per equivalent of carboxy groupspresent in the carboxy addition polymer.
 3. The method of claim 1wherein the cured film has a film weight of at least about 5 mg/in². 4.The method of claim 1 wherein the theoretical glass transitiontemperature of the carboxy addition polymer is about 50° C. to about100° C.
 5. The method of claim 1 wherein the epoxy resin includes aglycidyl polyether of bisphenol A.
 6. The method of claim 1 wherein thecarboxy addition polymer and the epoxy resin are reacted in the presenceof about 0.35 to about 1.0 equivalents of the tertiary amine perequivalent of carboxy groups present in the carboxy addition polymer. 7.The method of claim 1 wherein applying the aqueous coating compositionincludes roll coating, bar coating or spraying the aqueous coatingcomposition onto the substrate surface.
 8. The method of claim 1comprising heating the coated metal substrate at about 230° C. to about300° C.
 9. The method of claim 8 comprising heating the coated metalsubstrate at about 230° C. to about 300° C. for about 2 to about 20seconds.
 10. A composite material comprising a metal substrate having atleast one surface covered with a cured film formed by coating thesubstrate surface with an aqueous coating composition and heating thecoated substrate to form the cured film;wherein the aqueous coatingcomposition includes a least 30 wt. %, based on the weight of thecoating composition, of a film forming component which includes:A) aproduct formed by reacting a carboxy addition polymer and an epoxy resinin the presence of a tertiary amine, wherein the carboxy additionpolymer has a theoretical glass transition temperature of no more thanabout 110° C. and an acid number of at least about 200, and the epoxyresin has an epoxide equivalent wt. of at least about 1500; and B) aphenoplast resin having a melting point of no more than about 100° C.,wherein the composition has a viscosity of about 30 to about 60 secondsdetermined by #4 Ford cup at 80° F.
 11. The composite material of claim10 wherein the film forming component includes:A) a product formed byreacting at least about 10 wt. % of the carboxy addition polymer and atleast about 40 wt. % of the epoxy resin, wherein the epoxy resin has anepoxide equivalent wt. of about 1500 to about 5000 in the presence ofthe tertiary amine; and B) at least about 2 wt. % of the phenoplastresins; the wt. % of the carboxy addition polymer, the epoxy resin andthe phenoplast resin being based on the total weight of the carboxyaddition polymer plus the epoxy resin plus the phenoplast resin; andwherein the carboxy addition polymer and the epoxy resin are reacted inthe presence of about 0.35 to about 1.0 equivalents of the tertiaryamine per equivalent of carboxy groups present in the carboxy additionpolymer.
 12. The composite material of claim 10 wherein the cured filmhas a film weight of at least about 5 mg/in².
 13. The composite materialof claim 10 wherein the epoxy resin includes a glycidyl polyether ofbisphenol A.
 14. The composite material of claim 13 wherein the carboxyaddition polymer has a theoretical glass transition temperature of about50° C. to about 100° C.
 15. The composite material of claim 10 whereinthe carboxy addition polymer and the epoxy resin are reacted in thepresence of about 0.35 to about 1.0 equivalents of the tertiary amineper equivalent of carboxy groups present in the carboxy additionpolymer.
 16. The composite material of claim 10 wherein applying theaqueous coating composition includes roll coating, bar coating orspraying the aqueous coating composition onto the substrate surface.